Chlorophylls are involved in the conversion of sunlight into biochemical energy during the process of photosynthesis. Only a small fraction of the chlorophyll present participates in the basic photochemistry reaction. The remaining bulk of the chlorophylls performs a supportive but essential function of collecting the energy required by the reaction center. While the function of chlorophylls in the photosynthetic process is reasonably well defined, the structural organization of the light-harvesting chlorophylls in the thylakoid membrane is a subject of considerable current interest. This study proposes the use of high-field nuclear magnetic resonance spectroscopy (NMR) to study the structure and dynamics of lipids in the intact thylakoid membrane, and the specific interactions between chlorophyll and the lipids. A systematic study on the effects of acyl chain length, degree of unsaturation, and changes in polar headgroup in the model phospholipid bilayer on the interaction of chlorophyll a with the bilayer membrane will be carried cut to yield comparative information. Ancillary techniques will include optical spectroscopy and chromatography as requisite for the isolation, purification and purity determination of chlorophylls and lipids, and will include differential scanning calorimetry as adjunct to the NMR technique. The proposed research extends work carried out during the previous funding period on the organization of chlorophyll a in dimyristoylphosphatidylcholine bilayer membranes and in monogalactosyldiacylglycerols, a major galactolipid found in the thylakoid membrane. This study should yield useful information on the structure of the thylakoid membrane as well as the interaction, phase behavior and dynamics of chlorophyll a in model membrane systems.